The present invention relates to an apparatus for converting images of vehicle surroundings used for, for example, a driving support system for supporting driver's visibility.
Japanese Laid-Open Patent Publication No. Hei-11-328368 discloses an apparatus for converting images of vehicle surroundings used for helping the field of vision of a driver when the driver reverses up the vehicle into a garage, brings the vehicle closer to the roadside for parking, or drives the vehicle into a crossing or a T junction where the driver's visibility is poor.
This apparatus includes an electronic camera to photograph, for example, a rear view of the vehicle, or a blind corner view (front left or right view) of the vehicle. There is an increasing need for simultaneously providing the driver with multidirectional images around the vehicle. Under the situation, the driving support system employs a plurality of cameras to pick up images around the vehicle and provide the driver with a plurality of images side by side on a display.
The arrangement and operation of an apparatus for converting images of vehicle surroundings according to a related art will be explained. The related art in the following explanation employs VGA (video graphics array) of 640×480 pixels as an image output resolution of a camera and a display resolution presented for a driver.
To absorb a difference between the image data transmission rate of a camera and the processing speed of a CPU (central processing unit), the related art arranges an input frame buffer between the camera and the CPU. The input frame buffer has two banks for each camera, and the size of each bank is selected to cover an address space of 640×680 pixels of the camera. When a frame of image data is transmitted from the camera and is completely stored in one bank of the input frame buffer, the CPU carries out an image conversion process on the bank that has stored the image data. At the same time, the other bank of the input frame buffer is prepared for receiving the next frame of image data. These operations are repeated. From the bank of the input frame buffer on which the image conversion process has been conducted, the CPU reads image data according to addresses stored in a pattern memory and stores the read image data in an output memory.
When employing a plurality of cameras and displaying a plurality of images side by side on a single display, it is usual to partly thin images from the cameras and display the thinned images. If two cameras each of VGA size are employed, two systems of image data are provided from the cameras. These two systems of image data are thinned in a read process and the thinned image data is displayed on a display. To prevent images presented for the driver from flickering, the CPU usually displays a frame of image data after the image data is completely stored in the output memory.